Participants made visual lexical decisions to upper-case words and nonwords, and then categorized an
ambiguous N–H letter continuum. The lexical decision phase included different exposure conditions:
Some participants saw an ambiguous letter “?”, midway between N and H, in N-biased lexical contexts
(e.g., REIG?), plus words with unambiguousH(e.g., WEIGH); others saw the reverse (e.g., WEIG?,
REIGN). The first group categorized more of the test continuum as N than did the second group.
Control groups, who saw “?” in nonword contexts (e.g., SMIG?), plus either of the unambiguous
word sets (e.g., WEIGH or REIGN), showed no such subsequent effects. Perceptual learning
about ambiguous letters therefore appears to be based on lexical knowledge, just as in an analogous
speech experiment (Norris, McQueen, & Cutler, 2003) which showed similar lexical influence in
learning about ambiguous phonemes. We argue that lexically guided learning is an efficient general
strategy available for exploitation by different specific perceptual tasks.